Fuel cells are comprised of chemical reactors. The size of the chemical reactors put constraints on the ability to reduce the size of a fuel cell to micro-dimensions.
Existing fuel cells generally are a stacked assembly of individual fuel cells, with each stack producing high current at low voltage. The typical reactor construction involves reactant distribution and current collection devices brought into contact with a layered electrochemical assembly consisting of a gas diffusion layer, and a first catalyst layer. With the exception of high temperature fuel cells, such as molten carbonate cells, most proton exchange membrane, direct methanol, solid oxide or alkaline fuel cells have a layered planar structure where the layers are first formed as distinct components and then assembled into a functional fuel cell stack by placing the layers in contact with each other.
One major problem with the layered planar structure fuel cell has been that the layers must be held in intimate electrical contact with each other, which if intimate contact does not occur the internal resistance of the stack increases, which decreases the overall efficiency of the fuel cell.
A second problem with the layered planar structured fuel cell has been that with larger surface areas, problems occur to maintain consistent contact with both cooling and water removal in the inner recesses of the layered planar structured fuel cell. Also, if the overall area of the cell becomes too large then there are difficulties creating the contacting forces needed to maintain the correct fluid flow distribution of reactant gases over the electrolyte surface.
Existing devices also have the feature that with the layered planar structure fuel cell since both fuel and oxidant are required to flow within the plane of the layered planar structured fuel cell, at least 4 and up to 6 distinct layers have been required to form a workable cell, typically with a first flowfield, a first gas diffusion layer, a first catalyst layer, a first electrolyte layer, a second catalyst layer, a second gas diffusion layer, a second flowfield layer and a separator. These layers are usually manufactured into two separate fuel cell components and then a fuel cell stack is formed by bringing layers into contact with each other. When contacting the layers, care must be taken to allow gas diffusion within the layers while preventing gas leaking from the assembled fuel cell stack. Furthermore, all electrical current produced by the fuel cell in the stack must pass through each layer in the stack, relying on the simple contacting of distinct layers to provide an electrically conductive path. As a result, both sealing and conductivity require the assembled stack to be clamped together with significant force in order to activate perimeter seals and reduce internal contact resistance.
Electrical energy created in the fuel cell has to travel between layers of material compressed together before it can be used. These layers include membrane electrode assemblies, gas diffusion layers, and separator plates. The resistance to the transfer of electrical energy through each layer and between layers also affects the performance of the fuel cell. The contact pressure and contact area that can be achieved between the layers of the fuel cell stack are directly proportional to the conductivity of these components and hence the performance of the fuel cell stacks.
Laying out layers of material and compressing them together using the brute force approach of traditional fuel cell stacks is inefficient and expensive. In addition, such designs suffer from long term performance degradation because of thermal and mechanical cycles that occur during the operation of the fuel cells. A need has existed for less expensive and more efficient fuel cell layers.
In manufacturing fuel cell stack assemblies using this typical layering approach of all the components, it is difficult to accurately align the layers. Inaccurate alignment has a detrimental effect on the performance and durability of the fuel cell stacks.
A need has existed for a micro, or small fuel cells having high volumetric power density. A need has existed for micro fuel cells capable of low cost manufacturing because of having fewer parts than the layered planar structure fuel cell. A need has existed for a micro fuel cell having the ability to utilize a wide variety of electrolytes. A need has existed for a micro fuel cell, which has substantially reduced contact resistance within the fuel cell. A need has existed for a micro fuel cell, which has the ability to scale to high power has long been desired. A need has existed for micro fuel cells having larger reactant surface areas. A need has existed for fuel cells capable of being scaled to micro-dimensions. A need has existed for fuel cells capable of being connected together without the need for external components for connecting the fuel cells together.
A need has existed for a compact fuel cell with high aspect ratio cavities. The aspect ratio of the fuel cell is defined as the ratio of the fuel cell cavity height to the width. Increasing this aspect ratio is beneficial for increasing the efficiency of the fuel cell.
A need has existed to develop fuel cells topologies or fuel cell architectures that allow increased active areas to be included in the same volume, i.e. higher density of active areas. This will allow fuel cells to be optimized in a manner different than being pursued by most fuel cell developers today.